This application claims the benefit under 35 U.S.C. xc2xa7119, of Korean Patent Application No. 1999-11253, filed on Mar. 31, 1999, the entirety of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a method for manufacturing a polycrystalline silicon layer, and more particularly, to a system and a method for manufacturing a polycrystalline silicon layer for use in a thin film transistor (TFT) using a laser annealing technique.
2. Description of Related Art
In general, there are two methods for manufacturing an active layer for use in a polycrystalline thin film transistor (TFT). The first method involves depositing a polycrystalline material and patterning it to form a polycrystalline semiconductor layer as the active layer of the TFT. The other method involves depositing, patterning, and heat-treating an amorphous silicon layer to form a polycrystalline silicon layer as the active layer of the TFT using an excimer laser annealing technique or a furnace annealing technique.
In case of the former method, a polycrystalline silicon layer is used as the active layer and an impurity ion gas of a nitrogen group or a boron group is doped into both ends of the polycrystalline silicon layer to define source and drain regions. At this point, the polycrystalline silicon layer undergoes a laser annealing using a rare gas halide laser such as Ar, ArF, KrF, or XeCl to activate the gas doped into the source and drain regions. Laser annealing is also performed to recrystallize amorphous portions of the polycrystalline silicon layer formed due to energy generated when the impurity ion gas is doped.
In case of the latter method, first an amorphous silicon layer is deposited on a substrate using a sputtering technique. The layer then undergoes laser annealing to form the polycrystalline silicon layer.
As described above, the laser annealing is mainly used to manufacture the active layer for use in a polycrystalline thin film transistor or to activate the doped impurity ion gas to define the source and drain regions of the polycrystalline silicon layer.
FIG. 1 is a schematic view illustrating a configuration of a conventional laser annealing system.
The conventional laser annealing system includes a vacuum chamber 1 having a laser beam passage window 13 made of a transparent material such as a rock-crystal, a vacuum device 3 having a vacuum pump 31 and a vacuum tube 33 to place the vacuum chamber 1 in a specific atmosphere, for example, a vacuum or nitriding atmosphere, a laser device 5 that irradiates a laser beam with a predetermined energy through the laser beam passage window 13, and a stage 50 on which an amorphous silicon layer 23 on a substrate 21 as a workpiece is placed.
A method of manufacturing the polycrystalline silicon layer using the conventional laser annealing system described above will be explained.
First, the amorphous silicon layer 23 on the substrate 21 is located on the stage 50 in the vacuum chamber 1, and then the vacuum device 3 is operated to place the amorphous silicon layer 23 in a vacuum or nitride atmosphere. A laser beam is irradiated from the laser device 5 through the laser beam passage window 13 to scan the amorphous silicon layer 23 on the substrate 21 on the stage 50. At this point, the laser device 5 preferably produces about 200 to 300 laser beam pulses per second. As a result, the amorphous silicon layer 23 on the substrate 21 is converted into a polycrystalline silicon layer.
Furthermore, the impurity-doped ion gas defining the source and drain regions of the polycrystalline silicon layer is activated through the laser annealing technique described above.
In the vacuum method of the conventional art, as the number of shots increases, the layer quality increases. That is, the grain size becomes large, and the roughness of the surface can be improved as the number of shots is increased.
The conventional laser annealing system and the method for polycrystallization and activation described above have the following disadvantages: 1) the process takes a long time because the inside of the vacuum chamber 1 must be maintained in a specific atmosphere, for example, a vacuum or a nitriding atmosphere; 2) high-cost because a high-cost material such as a rock-crystal must be used for the laser beam passage window 13 and the vacuum device 3 is required; and 3) possible damage to the laser beam passage window 13 may result if part of the polycrystalline silicon layer 23 comes undone from the substrate 21. As shown in FIG. 2, a part 41 of the polycrystalline silicon layer 23 that comes undone may be deposited on the laser beam passage window 13 due to energy of the laser beam irradiated.
To overcome the problems described above, a preferred embodiment of the present invention provides a laser annealing system and a method for laser annealing that can be performed in a normal atmosphere and that forms a polycrystalline silicon layer having layer-sized crystals as an active layer of a thin film transistor.
In order to achieve the above object, the present invention provides a method for forming a polycrystalline semiconductor layer on a substrate at an atmospheric pressure, comprising: providing a chamber having an opening and a stage therein; forming an amorphous semiconductor layer on the substrate; positioning the amorphous semiconductor layer formed on the substrate on the stage of the chamber; and irradiating five to twelve laser beam shots to every position of a desired portion of the semiconductor layer over the stage through the opening of the chamber.
The present invention further provides a method for activating impurity-doped ion gas in a polycrystalline semiconductor layer on a substrate at an atmospheric pressure, comprising: providing a chamber having an opening and a stage therein; providing the polycrystalline semiconductor layer including a region having impurity-doped ion gas therein, the polycrystalline semiconductor layer being positioned on the substrate; positioning the polycrystalline semiconductor layer having the impurity-doped ion gas therein together with the substrate on the stage of the chamber; and irradiating five to twelve laser beam shots to every position of the region having the impurity-doped ion gas of the polycrystalline semiconductor layer over the stage through the opening of the chamber.
The laser beam includes one of a group consisting of Ar, ArF, KrF, and XeCl. The laser beams may be intermittently applied to the amorphous semiconductor layer, or the laser beams may be continuously applied to the amorphous semiconductor layer.